جستجوی مقالات مرتبط با کلیدواژه « روپلین » در نشریات گروه « زمین شناسی »

The Qom Formation, (Oligocene-early Miocene in age) consists of thick successions of marine marls, limestones, gypsum, and siliciclastics. It is deposited in the Sanandaj–Sirjan fore-arc basin, Urumieh-Dokhtar Magmatic Arc (Intra-arc basin), and Central Iran back-arc basin and it was subdivided into 11 members to date. "Unnamed member" which is identified by Nummulites intermedius and Eulepidina cf. dilatata and attributed to Rupelian, was introduced as the oldest member of the Qom Formation. Recent studies by the current author subdivided the Rupelian stage into “early Rupelian” and “late Rupelian”, based on the first appearances of lepidocyclinids in the latter one. Accordingly, the "unnamed member" is late Rupelian in age. Besides, the early Rupelian strata are characterized by the presence of Nummulites without lepidocyclinids, reported merely from southwestern and southern Kashan. The basal deposits of the Qom Formation sections in SW and S Kashan (composed of marl, limestone and marl limestone) are distinctly different from the “unnamed” member (alternation of silty marl, sandstone and limestone), “a” member (basal limestone) and “b” member (sandy marl) of the Qom Formation, in terms of lithology. Therefore, the mentioned deposits are introduced as a new member and named the "Verkan Member". Accordingly, the number of the Qom Formation members has increased to 12 and the “Varkan Member” (with 108-m thickness in the Varkan section and early Rupelian in age) is introduced as the oldest member of Qom Formation. The “Verkan Member” is present in the Varkan (SW Kashan), Vidoja (SW Kashan) and Ghohroud (S Kashan) sections.

The Asmari Formation is a thick carbonate sequence in the Zagros Foreland Basin that was deposited during the Oligo–Miocene. In order to conduct biostratigraphic studies, microfacies and to interpret the depositional environment, the Makhmal Kuh section in the Lurestan province located in west of Zagros was investigated. The section is 85 m thick, consisting of alternating layers of thick limestone interbedded with thin-layer limestone. Based on biostratigraphic studies, 12 genera belonging to 7 families of foraminifera were identified in the studied section. In this section, two fossil assemblages and 12 microfacies were identified based on the Rupelian-Aquitanian foraminifera distribution patterns. The fauna assemblages conform to the world standard zones. The study of microfacies indicates two different sedimentary sub-environments including lagoon and open sea in the studied section. These depositional sub-environments of the Asmari Formation are compatible with the inner, middle and outer ramp parts, formed under a Mesophotic, Oligophotic and Aphotic conditions in a homoclinal ramp.

The Asmari Formation at Nil anticline area has been studied in order to determine faunal assemblages، the age and the paleoecology. Paleontological and biostratigraphical studies led to the identification of 5 faunal assemblages. As a result، the age of the Asmari Formation in this section، with 291m thickness، is Rupelian/Chattian-Burdigalian. Extension of the large benthic foraminifera suggests that the Asmari Formation has been deposited in a shallow marine carbonate platform with tropical to subtropical and oligotrophy climatic condition. Based on faunal assemblage، the lower part of the Asmari Formation has been deposited in normal marine water conditions; while the upper part has been deposited in hypersaline waters. Diversity and the abundance of the benthic foraminifera، the rarity of coral debris and the absence of green algae show that the surface water temperature was low (below 20oc) during deposition of the Asmari Formation.

The Qom Formation deposits in the Bijegan area، northeast of Delijan، are Rupelian-Chattian in age، with a thickness of 162 meters. It consists of sandy limestone، thin to medium and thick bedded and massive limestone. It is disconformably overlain the Lower Red Formation. The upper boundary is covered by alluvium. 8 carbonate microfacies related to semi- restricted lagoon and open marine (slope) environments identified. Based on 120 thin section studied، microfacies analysis and field observation the Qom Formation in the study area deposited on an open shelf setting.

The uppermost layers of the Pabdeh Formation in Kuh e-Asmari section consist of microbial (tufa and stromatolite) facies interpreted to have been deposited in a lacustrine environment. These deposits are unconformably overlain by basal anhydrite and transitional zone of the Asmari and Pabdeh Formations. The transitional zone is correlated with the lower Asmari (with a basal unconformity or correlative conformity) in the Gachsaran No. 31 and Aghajari No. 61 wells and in Kuh e-Mish, Shahzadeh Abdullah, Tang-Sorgh and Rag-Sefid surface sections. Therefore the basal anhydrite and transitional zone should be considered as a part of the Asmari Formation. The drastic facies change near the Pabdeh and Asmari contact is due to thrust-loading, relative sea-level changes and climatic variations close to Ruplian-Chattian boundary.